1. Field of the Invention
This invention relates in general to copying devices and in particular to an original feed apparatus for an electrophotographic copying machine for copying an original in accordance with two copying systems including a sheet mode copying system and a book mode copying system.
2. Description of the Prior Art
In the sheet mode copying system, an original in sheet form, being transported by the feed apparatus is irradiated by conventional projection techniques for producing an electrostatic latent image of the subject matter by exposure using a slit. The original in sheet form is transported at a relatively low rate of 200 to 300 mm/sec, the rate varying depending on the magnification at which the copying of the original is effected. The original in sheet form is transported by the feed apparatus when it is illuminated for forming a latent image, so that no slip of the original should occur. On the other hand, in the book mode copying system, an original in sheet form or in the form of a document of large thickness, such as a book, is placed on a glass plate and scanned by an optical system while being irradiated for producing a latent image. When an original in sheet form is irradiated for producing a latent image in accordance with the book mode copying system, the original is transported on the glass plate by the feed apparatus at a relatively high rate of about 1000 mm/sec and stopped in a predetermined position on the glass plate as it abuts against a stopper. The stopper is moved away from the path of travel of the original both when the latter is moved forwardly after completion of irradiation thereof in the book mode copying system and when copying is carried out in accordance with the sheet mode copying system so that the stopper may not interfere with the transportation of the original in sheet form.
In order to avoid deformation or breakage of an original in sheet form when it abuts against a stopper or becomes jammed during its transportation in accordance with the book mode copying system, transportation of the original is customarily effected on the slack side of a conveyor belt by utilizing the loosening thereof. Thus the original can easily slip while being transported.
When the copying of a thin original is carried out in accordance with the sheet mode copying system in such a multi-mode copying machine, there is the tendency of "belt marks" being produced on the reproduction copy because background areas of the original transmits the light to the endless belts of the feed apparatus on which the original is being transported. The production of belt marks lowers the reproduction quality. When a copy sheet is larger in size than the original, it often happens that undesirable shadows of the belts are produced on side and end margins of the copy sheet. Further, in the copying machine of this type an original in sheet form should be fed exactly at a predetermined rate in the sheet mode copying system and prevented from deformation or breakage while being fed at a high rate in the book mode copying system.